1. Field of the Invention
The present invention relates to a printer and, more particularly, to a printer in which the printed image data exactly covers an entire sheet of paper without skewing or producing margins in the upper or lower portions of the paper sheet.
2. Description of the Related Art
There are many types of printers for printing image data on a sheet of paper. For example, there is known a thermal transfer printer comprising a thermal transfer head for generating heat responsive to image data, and an ink film disposed under the thermal transfer head, wherein the image data is printed on the paper sheet disposed under the thermal transfer head by the head and ink film. Especially, in a color thermal transfer printer, three resolved images of yellow, magenta and cyan are sequentially printed on the paper sheet to accomplish full coloring of the completed picture. In such a thermal transfer printer, the paper sheet is printed by sublimation of ink on the ink film which is heated by the thermal transfer head.
The printed matter resulting from such a thermal transfer printer is extremely clear. Therefore, the thermal transfer printer can be used for various applications. For example, after inputting image data into a computer via an image input device such as a scanner, a newly contrived picture can be created by revising and/or combining the input data according to a computer program and then may be outputted. Also, imaginary scenes and objects created with computer graphics, or the images of an electron microscope may be outputted using the thermal transfer printer. As this type of thermal transfer printer now tends to be used in lieu of photography in many fields, the printer should have the same or similar quality and form as a photograph.
FIG. 1A and FIG. 1B illustrate printing states on a paper sheet by a conventional printer. As shown in FIG. 1A, a picture 1 is printed on the paper sheet causing margins 2 in the upper and lower portions of the paper sheet. Also, the picture 1 may be printed askew on the paper sheet, as shown in FIG. 1B.
The causes of these problems will be described hereinafter taking a conventional platen-type printer as an example.
FIG. 2 and FIG. 3 show a perspective view and a side view for illustrating a printing operation by a conventional platen-type printer, respectively. As can be seen, a supplied paper sheet 7 is brought into contact with a drum 8 by a guide roller 5 disposed on the periphery of drum 8. The paper sheet 7 is transported, passing under a printing head 6 disposed above the drum 8, according to the rotation of the drum 8 and until the leading edge of the sheet reaches a guide roller 13. Then, image data is printed on the paper sheet 7 with an ink film 4 and the paper sheet 7 being pressed against the drum 8. Accordingly, when the paper sheet 7 is supplied askew between the drum 8 and the guide roller 5, it is inevitable for the paper sheet 7 to be printed in a skewed state. Further, a margin extending by a distance D from an initial printing position 10 to the guide roller 13 is created in the leading edge portion of the paper sheet 7.
In addition, to prevent the paper sheet 7 from sliding in its proceeding direction and coming off the drum 8, a plurality of guide rollers 5, 13 and 14 are provided around the drum 8 as shown in FIG. 2 and FIG. 3, which increases the manufacturing cost of the printer.
The above-described margins in printed paper sheets, or the skewed printing thereon, causes a low quality appearance in the printed paper sheets, thereby resulting in wasted paper.